In order to reduce fuel consumption and a NOx emission, JP-2007-16777A (U.S. Pat. No. 7,210,457B2) and JP-2008-69788A (U.S. Pat. No. 6,994,073B2) show that an internal combustion engine is driven by a self-ignited combustion in which the air-fuel mixture is self-ignited to be combusted. Generally, in the self-ignited combustion, a combustion condition control is difficult and a stabilization of combustion condition is hard, compared with a spark-ignited combustion.
In a technology disclose by JP-2007-16777A and JP-2008-69788A, base on a characteristic in which an ion current is generated according to a combustion state of the air-fuel mixture, the self-ignited combustion condition is detected by detecting the ion current. Based on the detected combustion condition, a fuel injection quantity and a fuel injection timing are controlled in order to stabilize the self-ignited combustion condition.
However, in a system where the self-ignited combustion condition is detected to control the fuel injection quantity and the fuel injection timing based on the detected combustion condition, if the combustion condition in a combustion cycle is deteriorated, after a deterioration in the combustion condition is actually detected, the fuel injection quantity and the fuel injection timing are controlled in order to restrict the deterioration in combustion in a subsequent combustion cycle. Thus, it is likely that the control of the combustion condition is delayed and the self-ignited combustion can not be stabilized sufficiently.